The extreme infrared (IR) luminosity of local luminous and ultra-luminous IR
galaxies (U/LIRGs; 11 < log LIR /Lsun < 12 and log LIR /Lsun > 12,
respectively) is mainly powered by star-formation processes triggered by
mergers or interactions. While U/LIRGs are rare locally, at z > 1, they become
more common, they dominate the star-formation rate (SFR) density, and a
fraction of them are found to be normal disk galaxies. Therefore, there must be
an evolution of the mechanism triggering these intense starbursts with
redshift. To investigate this evolution, we present new optical SWIFT integral
field spectroscopic H{\alpha}+[NII] observations of a sample of 9
intermediate-z (0.2 < z < 0.4) U/LIRG systems selected from Herschel 250{\mu}m
observations. The main results are the following: (a) the ratios between the
velocity dispersion and the rotation curve amplitude indicate that 10-25% (1-2
out of 8) might be compatible with being isolated disks while the remaining
objects are interacting/merging systems; (b) the ratio between un-obscured and
obscured SFR traced by H{\alpha} and LIR, respectively, is similar in both
local and these intermediate-z U/LIRGs; and (c) the ratio between 250{\mu}m and
the total IR luminosities of these intermediate-z U/LIRGs is higher than that
of local U/LIRGs with the same LIR . This indicates a reduced dust temperature
in these intermediate-z U/LIRGs. This, together with their already measured
enhanced molecular gas content, suggests that the interstellar medium
conditions are different in our sample of intermediate-z galaxies when compared
to local U/LIRGs.

On the Observed Diversity of Star Formation Efficiencies in Giant
Molecular Clouds

Observations find a median star formation efficiency per free-fall time in
Milky Way Giant Molecular Clouds (GMCs) on the order of $\epsilon_{\rm ff}\sim
1\%$ with dispersions of $\sim0.5\,{\rm dex}$. The origin of this scatter in
$\epsilon_{\rm ff}$ is still debated and difficult to reproduce with analytical
models. We track the formation, evolution and destruction of GMCs in a
hydrodynamical simulation of a Milky Way-like galaxy and by deriving cloud
properties in an observationally motivated way, measure the distribution of
star formation efficiencies which are in excellent agreement with observations.
We find no significant link between $\epsilon_{\rm ff}$ and any measured global
property of GMCs (e.g. gas mass, velocity dispersion). Instead, a wide range of
efficiencies exist in the entire parameter space. From the cloud evolutionary
tracks, we find that each cloud follow a \emph{unique} evolutionary path which
gives rise to wide diversity in all properties. We argue that it is this
diversity in cloud properties, above all else, that results in the dispersion
of $\epsilon_{\rm ff}$.